1. Field of the Invention
The present invention relates to a composition for an electroluminescent (EL) element, and more particularly to a composition for an organic EL element, and a method of manufacturing the organic EL element.
2. Description of the Background Art
An organic EL element has a constitution in which a cathode and an anode are connected to the opposite sides of a solid thin film containing a fluorescent organic compound. When a voltage is applied across the electrodes, electrons and holes are injected into the thin film, and they migrate according to the generated electric field and recombine with each other. At the time, excitons are produced by the energy liberated upon the recombination, and energy (in the form of fluorescence or phosphorescence) is emitted when the excitons are returned to the ground state thereof. This phenomenon is called electroluminescence.
The characteristic of an organic EL element resides in the point that a high luminance surface emission of 100 to 100,000 cd/m2 is possible at a low voltage of less than about 10V. Further, since organic compounds are used, there is an unlimited possibility as to the selection of the raw materials. This is the excellent advantage of the EL element, which cannot be found in other material systems. For example, by appropriate selection of the kinds of the fluorescent materials, it is possible to provide emission of visible rays ranging from blue color to red color.
In this connection, the luminescence efficiency and the stability of the EL element which are important factors of the EL element are achieved by a luminescent layer. In the past, doping of high efficiency fluorescent dyes into the luminescent layer has been carried out in order to improve the luminescence efficiency and change the emission wavelength.
The conventional organic EL element is formed into a thin film laminated-type organic thin film EL element, in which a low molecular material (host material) is mainly used as an organic EL material so that the thin film is formed of the low molecular material. Such an organic EL material is formed by adding a fluorescent dye to a low molecular weight host material. Examples of such an EL element include an element obtained by adding a fluorescent dye such as perylene or distyrylbiphenyl to a host material such as aluminum quinolynol complex (Alq3) or distyrylbiphenyl or the like.
In order to form a thin film from such a low molecular dye compound, a vapor deposition method has been so far employed. However, it is difficult to obtain a homogeneous defect-free thin film by the vapor deposition method. Further, the vapor deposition is not an efficient method, since it takes a long time to form several organic layers by the method.